The invention relates to a clutch arrangement for transmitting a drive torque from a drive shaft to an ancillary unit, in particular to a fan wheel, of a motor vehicle, comprising a drive shaft, an output, and a friction disc clutch which is able to be switched by means of an electromagnet arrangement. The invention further relates to an actuation method for actuating such a clutch arrangement.
Single-stage or multi-stage friction disc clutches are basically known for driving ancillary units such as fan wheels. Such friction disc clutches, constructed for example as clutches which are able to be activated electromagnetically, are described for example in EP 0 317 703 A2, DE 32 031 43 C2 and DE 42 07 710 A1. Reference is to be made to these publications with regard to the basic structure, the mode of operation and the field of use of such friction disc clutches. Friction disc clutches have no slip on engagement and therefore no differential rotation speed on the bearing site. It is also generally known that through the lack of rolling of the rolling bodies, this can lead to an increased abrasion and hence to an increased wear up to the possible failure of the bearing sites in field applications. In particular in the case of single-stage friction disc clutches, it is disadvantageous that in the engaged (coupled or respectively connected) state at high input rotation speeds these often provide undesirably high output rotation speeds and intensive switching jolts occur.
Instead of the previously described friction disc clutches, so-called fluid friction clutches, also designated as visco clutch or viscosity clutch, are used for the driving of ancillary units of motor vehicles. In visco clutches, a rotational movement is transferred from a primary side to a fluid, and then from the latter to a secondary side of the clutch. With regard to a possible structure of fluid friction clutches, reference is to be made to U.S. Pat. No. 4,305,491, EP 1 248 007 B1 and DE 699 11 479 T2. Most fluid friction clutches in commercial use comprise a hydraulic control valve, by which the slip of the fluid friction clutch is able to be set. In simple variant embodiments, the opening cross-section of the control valve is set via a temperature-detecting bimetal element. In addition, control vales constructed as an electromagnetic valve are known, which control the fluid flow between a storage chamber and a working chamber and therefore control the slip of the fluid friction clutch. Basically it is known to construct the hydraulic control valves as proportional valves or alternatively as discrete vales operated in a clocked manner, in which the through-flow quantity is dependent on the ratio of the opened time component to the closed time component of the armature.
In contrast to single-stage friction disc clutches, fluid friction clutches have a slow response behaviour and are afflicted by high slip values. Proceeding from the above-mentioned prior art, the invention is based on the problem of indicating an alternative clutch arrangement, which is distinguished by a smaller amount of wear of the friction disc clutch. In particular, the clutch arrangement is to manage with as few functional components as possible. In particular, the clutch arrangement is to be distinguished by being able to be actuated comfortably. Preferably, a variable speed adjustment is to be guaranteed over a large range, and also good damping characteristics and a quick response behaviour, preferably with full possibility for connection through. The problem further consists in indicating a simplified actuation method for such a clutch arrangement.